ospf6d: Fix crash because neighbor structure was freed

The loading_done event needs a event pointer to prevent
use after free's.  Testing found this:

    ERROR: AddressSanitizer: heap-use-after-free on address 0x613000035130 at pc 0x55ad42d54e5f bp 0x7ffff1e942a0 sp 0x7ffff1e94290
    READ of size 1 at 0x613000035130 thread T0
        #0 0x55ad42d54e5e in loading_done ospf6d/ospf6_neighbor.c:447
        #1 0x55ad42ed7be4 in event_call lib/event.c:1995
        #2 0x55ad42e1df75 in frr_run lib/libfrr.c:1213
        #3 0x55ad42cf332e in main ospf6d/ospf6_main.c:250
        #4 0x7f5798133c86 in __libc_start_main (/lib/x86_64-linux-gnu/libc.so.6+0x21c86)
        #5 0x55ad42cf2b19 in _start (/usr/lib/frr/ospf6d+0x248b19)

    0x613000035130 is located 48 bytes inside of 384-byte region [0x613000035100,0x613000035280)
    freed by thread T0 here:
        #0 0x7f57998d77a8 in __interceptor_free (/usr/lib/x86_64-linux-gnu/libasan.so.4+0xde7a8)
        #1 0x55ad42e3b4b6 in qfree lib/memory.c:130
        #2 0x55ad42d5d049 in ospf6_neighbor_delete ospf6d/ospf6_neighbor.c:180
        #3 0x55ad42d1e1ea in interface_down ospf6d/ospf6_interface.c:930
        #4 0x55ad42ed7be4 in event_call lib/event.c:1995
        #5 0x55ad42ed84fe in _event_execute lib/event.c:2086
        #6 0x55ad42d26d7b in ospf6_interface_clear ospf6d/ospf6_interface.c:2847
        #7 0x55ad42d73f16 in ospf6_process_reset ospf6d/ospf6_top.c:755
        #8 0x55ad42d7e98c in clear_router_ospf6_magic ospf6d/ospf6_top.c:778
        #9 0x55ad42d7e98c in clear_router_ospf6 ospf6d/ospf6_top_clippy.c:42
        #10 0x55ad42dc2665 in cmd_execute_command_real lib/command.c:994
        #11 0x55ad42dc2b32 in cmd_execute_command lib/command.c:1053
        #12 0x55ad42dc2fa9 in cmd_execute lib/command.c:1221
        #13 0x55ad42ee3cd6 in vty_command lib/vty.c:591
        #14 0x55ad42ee4170 in vty_execute lib/vty.c:1354
        #15 0x55ad42eec94f in vtysh_read lib/vty.c:2362
        #16 0x55ad42ed7be4 in event_call lib/event.c:1995
        #17 0x55ad42e1df75 in frr_run lib/libfrr.c:1213
        #18 0x55ad42cf332e in main ospf6d/ospf6_main.c:250
        #19 0x7f5798133c86 in __libc_start_main (/lib/x86_64-linux-gnu/libc.so.6+0x21c86)

    previously allocated by thread T0 here:
        #0 0x7f57998d7d28 in __interceptor_calloc (/usr/lib/x86_64-linux-gnu/libasan.so.4+0xded28)
        #1 0x55ad42e3ab22 in qcalloc lib/memory.c:105
        #2 0x55ad42d5c8ff in ospf6_neighbor_create ospf6d/ospf6_neighbor.c:119
        #3 0x55ad42d4c86a in ospf6_hello_recv ospf6d/ospf6_message.c:464
        #4 0x55ad42d4c86a in ospf6_read_helper ospf6d/ospf6_message.c:1884
        #5 0x55ad42d4c86a in ospf6_receive ospf6d/ospf6_message.c:1925
        #6 0x55ad42ed7be4 in event_call lib/event.c:1995
        #7 0x55ad42e1df75 in frr_run lib/libfrr.c:1213
        #8 0x55ad42cf332e in main ospf6d/ospf6_main.c:250
        #9 0x7f5798133c86 in __libc_start_main (/lib/x86_64-linux-gnu/libc.so.6+0x21c86)

Add an actual event pointer and just track it appropriately.

Signed-off-by: Donald Sharp <sharpd@nvidia.com>
(cherry picked from commit 77e838e)

ospf6d/ospf6_message.c

@@ -2522,7 +2522,8 @@ void ospf6_lsreq_send(struct event *thread)
 
 	/* schedule loading_done if request list is empty */
 	if (on->request_list->count == 0) {
-		event_add_event(master, loading_done, on, 0, NULL);
+		event_add_event(master, loading_done, on, 0,
+				&on->event_loading_done);
 		return;
 	}
 

ospf6d/ospf6_neighbor.c

@@ -173,6 +173,7 @@ void ospf6_neighbor_delete(struct ospf6_neighbor *on)
 	EVENT_OFF(on->thread_send_lsack);
 	EVENT_OFF(on->thread_exchange_done);
 	EVENT_OFF(on->thread_adj_ok);
+	EVENT_OFF(on->event_loading_done);
 
 	EVENT_OFF(on->gr_helper_info.t_grace_timer);
 
@@ -428,7 +429,8 @@ void ospf6_check_nbr_loading(struct ospf6_neighbor *on)
 	if ((on->state == OSPF6_NEIGHBOR_LOADING)
 	    || (on->state == OSPF6_NEIGHBOR_EXCHANGE)) {
 		if (on->request_list->count == 0)
-			event_add_event(master, loading_done, on, 0, NULL);
+			event_add_event(master, loading_done, on, 0,
+					&on->event_loading_done);
 		else if (on->last_ls_req == NULL) {
 			EVENT_OFF(on->thread_send_lsreq);
 			event_add_event(master, ospf6_lsreq_send, on, 0,

ospf6d/ospf6_neighbor.h

@@ -123,6 +123,7 @@ struct ospf6_neighbor {
 	struct event *thread_send_lsack;
 	struct event *thread_exchange_done;
 	struct event *thread_adj_ok;
+	struct event *event_loading_done;
 
 	/* BFD information */
 	struct bfd_session_params *bfd_session;